1. Field of the Invention
The present invention relates to a negative type photoresist developing apparatus and particularly, to a developing apparatus to be used for developing a negative type photoresist in a photolithographic process in manufacturing of a semiconductor device.
2. Description of the Prior Art
Generally, a photoresist is used for selectively etching a semiconductor or an oxide film. In the prior art, developing apparatus for developing an exposed photoresist film is known. For example, Japanese Patent Laid-Open Gazette No. 52132/1982 discloses a semiconductor manufacturing apparatus in which a CPU controls the number of revolutions of a rotating head for placing an exposed semiconductor wafer and the flow rate of a developer to be supplied to the semiconductor wafer so that development can be applied to the semiconductor wafer correctly and in a short period after the exposure of a photoresist film.
FIG. 1 is an illustration showing an example of a conventionaly utilized negative type photoresist developing apparatus using a spray system.
In FIG. 1, a conventional negative type photoresist developing apparatus comprises a developer tank 1, a rinse solution tank 2, a developer feed pipe 3, a rinse solution feed pipe 4, a developer pump 5, a rinse solution pump 6, a developer nozzle 7, a rinse solution nozzle 8, a motor 9 and a specimen table 10. On the specimen table 10, there is placed a specimen 11 having a negative type photoresist film exposed in advance through a specified pattern. A developer is drawn up by the developer pump 5 from the developer tank 1 and sprayed onto the specimen 11 through the developer nozzle 7. The spraying of the developer continues for a fixed period and during the spraying, the motor 9 is generally driven to rotate the specimen 11 so that the developer may be spread evenly. After a lapse of the fixed period, a rinse solution is drawn up by the rinse solution pump 6 from the rinse solution tank 2 and sprayed onto the specimen 11 through the nozzle 8. At this time also, the specimen 11 is rotated.
FIG. 2 is a graph showing changes, according to the passage of time, in the flow rates of the developer and the rinse solution supplied to a photoresist by the conventional negative type photoresist developing apparatus shown in FIG. 1.
In a developing step (a) shown in FIG. 2, the photoresist in the non-exposed regions of the specimen 11, where cross-linking does not proceed dissolves completely in the developer. On the other side, the developer also penetrates into the exposed portions where cross-linking is developed, and dependent on the state of the cross-linking, those exposed photoresist portions also dissolve a little. In addition, the exposed photoresist portions absorb the developer and the volumes thereof are increased considerably. In a developing step (c) shown in FIG. 2, the swelling photoresist portions are contracted by the rinse solution. The change of the volume by this contraction is defined by the energy of the ultraviolet rays, X rays or electron beam applied to the photoresist film.
As described above, in the developing process of a conventional negative type photoresist film, the photoresist film swells considerably by the developer sprayed thereon and then contracts by the rinse solution sprayed thereon subsequently. The photoresist portions where cross-linking is accelerated undergo a stress due to this abrupt contraction. On account of this stress, the pattern obtained after the developing process has an inferior precision and accordingly, it is difficult to form fine patterns using the conventional apparatus.
In addition, for the purpose of mitigating the stress due to the abrupt change from the swelling to the contraction, a step (b) shown in FIG. 2 may be applied so that the developer and the rinse solution can be sprayed simultaneously. However, such step has little effect for mitigating the stress and it is still extremely difficult to form fine patterns.
Furthermore, in order to solve the above described problems, a method for continuously changing the flow rates of the developer and the rinse solution in the developing process may be considered. However, in a conventional negative type photoresist developing apparatus, the flow rates of the developer and the rinse solution are defined by the capacities of the developer pump 5 and the rinse solution pump 6 and the diameters of the nozzles 7 and 8 and as a result, the flow rates cannot be changed.